Severe Weather Criteria

Detailed Severe Weather Assessments Across the South Island

We use a meticulous approach to understanding the diverse climatic conditions across the South Island. Our team of seasoned forecasters conducts comprehensive region-by-region assessments to evaluate the potential impact of impending severe weather events.

For example, we recognize that the Westland Region is accustomed to persistent and heavy rain, whereas Christchurch typically experiences distinct weather patterns. Taking this into account, a rainfall of 125–150mm over 24 hours may have a limited disruptive effect on the West Coast but could lead to substantial flooding further east.

Our assessments consider various factors, including soil moisture, enabling us to fine-tune the risk levels. In this scenario, the West Coast would see an enhanced risk of significant rain, while Christchurch would face a high likelihood of impactful weather during the same event.

This tailored approach ensures our risk determinations are finely tuned to the specific conditions of each South Island region, providing accurate and detailed forecasts customized to the unique needs of every area.


Date: 28/07/2025

Risk Levels and Colour Coding

We issue our Significant Weather Outlook daily to indicate the possibility of significant or impactful weather.

Our risk levels are colour-coded to indicate the severity and likelihood of potential weather impacts. These levels are tailored to reflect localised conditions, ensuring communities receive accurate and relevant information to help prepare for severe weather events.

Slight Risk (Yellow)

  • Probability: Less than 30% (but not zero) chance of impactful severe weather within the highlighted area.

  • Description: While the probability is low, weather-related impacts are still possible and warrant monitoring.

Enhanced Risk (Orange)

  • Probability: 30–50% chance of impactful severe weather within the highlighted area.

  • Description: Conditions suggest an increased likelihood of weather-related impacts. Preparedness is advised.

High Risk (Red)

  • Probability: 50–70% chance of impactful severe weather within the highlighted area.

  • Description: A high risk indicates a strong potential for significant weather impacts. Special Weather Statements will likely be issued to alert the public.

Critical Risk (Purple)

  • Probability: At least 70% confidence in the occurrence of significant weather impacts.

  • Description: Reserved for the most severe and high-impact weather events. A detailed Critical Risk Forecast will be issued to provide specific guidance and response recommendations.